Process of making sodium ferrocyanid.



UNITED STATES.

twins 1 oFFIoE.

ALEXANDER R. TILLINGHAST, OF SOLVAY, NEW YORK, ASSIGNORTO SEMET- OLVAY COMPANY, OF SOLVAY, NEW YORK,-A CORPORATION OF NEW YORK.

PROCESS OF MAKING SODIUM FERROGYANID.

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To all whom it may concern:

' ."Be it known that I. ALEXANDER Ii. Tn.- muonas'r, a citizen 0,1 the United States, residing at Solvay. in the countyot' Onon daga and State of New York. have. invented certain new and useful ln'q'n'ovements in Processes of Making Sodium l errocyanid, of which the following is a specification.

As is well. known sodium ferrocyan'u. may be formed by scrubbing gas containing cyanogen, such as the gas resulting from the destructive distillation of coal, with water containing ferrous hydrate or ferrous carbonate, or both. in suspension and having soda ash (N CO in solution.

In an application for Letters Patent filed by me December 20, 1916, SeriaLNo. 107.970, I have described a process for the making of sodium ferrocyanid which is particularly characterized by treating the solution of sodium ferrocyanid formed upon scrubbing the gas as above stated with milk of lime to convert the soda ash remaining in solution into more soluble caustic soda, and break up insoluble ferrocyanids formed in the scrub bing. In such process upon crystallizing out of solution the sodium ferrocyanid formed, caustic soda and a residue of sodium carbonate will remain in solution in the mother liquor with the uncrysta'llized so dium ferrocyanid, and upon further con centration of the mother liquor someof thesodium compounds will crystallize out ahead '.-'0f the ferr eyan'id thus giving an impure product. The object of my present invention is to enable the complete recovery of the sodium ferro'cyanid in the solution in a simple and inexpensive manner and without contamination and at the same time to recover and utilize the caustic soda'remaining in the mother liquor.

To this end, after the sodium ferrocyanid hasbeen crystallized out of the formed so 'lution thereof as completclyas may be without also throwing out impurities, which may be done in 'anyn'sual' or suitable well'known manner, the mother liquor is added to a solution of copper-as (ferrous sulfate) by combination with which the sodium ferroeyanid is converted into insoluble ferrous ferrocyanid whilewith the caustic soda and sodium carbonate are formed respectively ferrous Specification of Letters Patent.

Patented J an. 8, 1918.

Application filed January 10, 1917. Serial No. 141,540.

the ferrous hydrate and ferrous carbonate being used in repeating th'e'process.

Additional ferrous hydrate or carbonate for the purpose i provided by treating cop peras with caustic soda or sodium carbonate. The cyanogen containing gas, from which the ammonia has been removed so far as practicable, is then scrubbed in a suspension of the ferrous hydrate and carbonate (washed clean of sodium sulfate), together with the intermixed ferrous ferrocyanid, in a solution of soda ash. Upon scrubbing the gas sodium ferrocya'nid is formed by combination of cyanogen in the gas with the fer" rous hydrate and ferrous carbonate.

The liquor from the scrubber contains sodium ferrocyanid, which is in solution, soda ash in solution, two thirds of which exists as sodium bicarbonate, a large excess of ferrous sulfid in the form of a black, insoluble sludge, a considerable quantity of insoluble ammonia ferrocyanid, due to the presence of nnseparated ammonia in the gas, the insoluble ferrous ferrocyanid formed by the combination of the sodium terrocyanid in the mother liquid with the ferrous sulfate and possibly small quantities of other insoluble ferrocyanids.

lo order. to convert the insoluble ferrocyanids into the soluble form, milk of lime is added to the mixture'which is then boiled,

and allowed to settle. .The amount of lime" added is. such as is. necessary to effect the y desired reaction, 6., on an average from .1 to .5of :1 pound of milk of lime to each gallon of liquor. The lime converts the bi carbonate and sodium carbonate present into caustic soda which in turn converts the in- :soluble ferrocyanids into soluble ferrocyanid as, for example, according to' the reaction.

i u o-s aomi cyanid from the cyanogen content of gas,

the method of recm'ering from a mother liquor from which sodium ferrocyanid has been crystallized the-rosettes of; sodium ferrohe used in repeatcyanid and caustic soda and sodium carbonate contained therein which consists in treating ferrous sulfate with the mother liquor whereby the sodium ferrocyanid is converted into ferrous ferrocyanid and the caustic soda and sodium carbonate form ferrous hydrate and ferrous carbonate forming a suspension of the ferrous ferrocyanid, ferrous hydrate and ferrous carbonate in a solution of soda ash and scrubbing cyanogen containing gas therewith in .a repetition of the process, and finally treating the resultin}; solution with milk of limeto convert the insoluble ferrous ferrocyanid into sodium ferrocyanid.

In estimony whereof I have afiixed my signature, this 8th day or January, 1917.

AL ANDER 7e. TILLINGHAS 

